Drum component for volute compass

Silver drum from a volute compass, designed by David Lyle, Europe, 1760. Cylindrical shaped with turning screw on the side

Volute compass with shagreen case, 1760. The instrument was presented to King George III in 1760 by David Lyle, who designed it. The volute compass is similar in principle to a beam compass except that the pencil in the slider is not fixed but moves with respect to the stationary point as the compass is turned. The compass operates by turning the beam round the fixed point in such a manner that the large screw head remains in one orientation. If this is the case the slider will be moved down the beam at a rate in proportion to the beam's rotation, causing a spiral to be drawn. The various drums give various spirals. The apparatus was designed in 1760 by David Lyle.